Weimann has congratulated Villa on winning promotion to the Premier League, and the 27-year-old, who can operate as a forward or as a winger, has commiserations for Derby.
Anwar El Ghazi put Villa in the lead after 44 minutes, and John McGinn doubled the advantage on 59 minutes.
Derby halved the deficit on 81 minutes when Martyn Waghorn found the net, but the Villans held on for the win.
The result means that Villa will play in the Premier League next season, while Derby will stay in the Premier League.
Weimann started his professional club football career at Villa and was on the books of Derby from 2015 until 2018 before he joined City in the summer of 2018 for a transfer fee reported by The Bristol Post to be worth £2 million, and the Austria international has sent a message to the Villans and the Rams on Twitter.
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