import re
regex = r"https?://myhost\.mydomain\.(?:com|io)/\S*?(https?://myhost\.mydomain\.(?:com|io)/\S*\.(?:jpe?g|png))"
test_str = ("https://m...content-available-to-author-only...n.com/pnLVyL7HjrxMlxjBQkhcOMr2WUs=/400x400/https://m...content-available-to-author-only...n.com/images/98f9a734-52e2-4616-adf7-bf0165bbf738.png")
matches = re.search(regex, test_str)
if matches:
print(matches.group(1))
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