While Mike Ashley's reign as Newcastle United owner has not exactly been short of calamities, there are few deals which better illustrate just how poor the 57-year-old's business in the transfer market has been than the sale of Adam Armstrong.

Indeed, in spite of scoring an impressive 17 goals and registering five assists over his 26 appearances for the Magpies' under-23 side, Ashley decided to sanction the sale of the striker upon receiving an offer of £1.71m from Blackburn Rovers in the summer of 2018 - a figure just £360,000 above his Transfermarkt value at the time. That was despite the fact that the club's top league goalscorer in the season prior was Ayoze Perez with a mere eight goals.

Subsequently, and rather unsurprisingly, Armstrong went on to enjoy a fine season with Rovers in the following campaign, scoring five goals, registering three assists and creating six big chances over his 44 Championship appearances - returns which saw the 24-year-old average a SofaScore match rating of 6.69.

However, the former England under-21 international really began to find his feet in the division over his 46 league appearances in 2019/20, scoring 16 goals, providing six assists and creating seven big chances for his teammates, as well as earning a seasonal SofaScore match rating of 6.83.

The centre-forward continued his meteoric upward trajectory over his 40 Championship appearances last season, scoring a whopping 28 goals, registering five assists and creating seven big chances for his teammates, seeing the forward earn a rather remarkable average SofaScore match rating of 7.20.

This form convinced Southampton to spent £15.93m of their summer transfer budget on the former Blackburn star, ensuring that the 24-year-old will be plying his trade in the Premier League this season - all just three years after leaving Newcastle.

Dubbed a "special" talent by former Ewood Park team-mate Richie Smallwood, now valued at £16.2m by Transfermarkt and having already scored his first league goal for Saints, it would certainly appear as if Ashley's decision to sell the £17k-per-week striker for peanuts back in 2018 has turned into something of a transfer nightmare from the Magpies owner.

In other news: Ashley must sanction Newcastle swoop for £9m-rated beast in January, he'd be a big coup