Chelmsford-born Hayden spent eight years with the Gunners, progressing through the youth ranks to make two first-team appearances, both in the League Cup.

However, since signing for Newcastle in the summer of 2016, he's won a Sky Bet Championship title winners' medal, become an England under-21 international and now established himself as a Premier League player, with his first top-flight goal coming at Southampton in October.

And Mertesacker - speaking in the Arsenal matchday programme for Saturday's game - said: "He's a great character and was a great kid, who always loved to compete.

"He was always hard on himself and hard on his team-mates. I always thought he could make it because of his character, because of his attitude.

"Technically he had a lot too, which explains why he's been able to make the adaption from playing as a centre back to playing as a number six. That shows how good he is with the ball."

Hayden has made 15 appearances in the Premier League so far this term, and recently played his 50th game for Newcastle.

And former Germany international Mertesacker added: "I love seeing him have a chance in the Premier League. Not everyone gets that opportunity to leave Arsenal and find another team in the Premier League, and then come back to the Emirates as a starter for the opposition.

"That's what Isaac's done. He's just continuing what he showed here and what I really like is his consistency. He doesn't give up, he’s raised his game and I'm really happy for him."

The Arsenal matchday programme will be on sale from around the Emirates before Saturday's game, priced at £3.50.